Lord Narasimhadeva is the fourth of the 10 avatars (incarnations) of the Hindu god Krishna. The demon Hiranyakashipu, twin brother of the demon overthrown by Vishnu in his previous incarnation as Varaha, obtained a boon from the god Brahma that he could not be killed by man or beast, from inside or outside, by day or by night, and that no weapon could harm him. Thus, feeling secure, he began to trouble heaven and earth. His son, Prahlada, on the other hand, was a devotee of Vishnu, even though his father threatened his life because of it. One day the demon challenged Prahlada and, kicking a stone pillar, asked: “If your god is omnipresent, is he in this pillar also?” Krishna emerged from the pillar in the form of a man-lion and slew the demon at dusk on the threshold. Thus, this is the day that he comes to save his devotee, Prahlada..http://www.britannica.com/EBchecked/topic/403407/Narasimha